Add README file and improve usage message

Nagios plugin to check lock file state
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This plugin check lock file statue.
Usage
-----
Usage : ./check_lock_file -l /path/to/lock.file [-o uid] [-w W] [-c C] [-d] [-h]
Check lock file status
Parameters :
-l /path/to/lock.file Path to lock file
-o uid Valid lock file owner (optional)
-w W Exit with WARNING status if lock file
has been created for more than W hours
-c C Exit with CRITICAL status if lock file
has been created for more than C hours
-d Enable debug mode
-h Show this message
Copyright
---------
Copyright (c) 2014 Benjamin Renard
License
-------
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License version 2
as published by the Free Software Foundation.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.